The investigation of a role for TRPV1 at a remote site in sepsis

Little is known about the innate protective mechanisms against the onset of sepsis the exaggerated host response to infection. There is evidence that transient receptor potential vanilloid 1 (TRPV1) exerts a protective role on lipolysaccharide (LPS)-induced sepsis as TRPV1-/- mice show an exacerbated sepsis with increased levels of tumour necrosis factor-α and nitric oxide in the peritoneal cavity. We have investigated whether there are differences in leukocyte-endothelial interactions and microvascular permeability in early and late sepsis in TRPV1+/+ (WT) and TRPV1-/- (KO) mice. All procedures were conducted in accordance with the Animals (Scientific Procedures) Act 1986 and the mice (25-35 g; n = 6-10) were kept in a climatically controlled environment and given food and water ad libitum. They received 11.25 x 106 endotoxin units.kg-1 i.p. or 0.9% saline i.p. and were anaesthetised with a mixture of ketamine (100mg.kg-1) and xylazine (10mg.kg-1, i.p.) at 4hrs (early sepsis) or 18hrs (late sepsis). The cremaster muscle was prepared under the microscope to quantify leukocyte rolling, adhesion and transmigration in vivo. Ex vivo permeability measurements were carried out post mortem (Schedule 1). The aorta was cannulated, blood was flushed from the preparation and the cremaster perfused with Krebs buffer solution containing albumin and FITC-albumin (10 mg.ml-1 each). Permeability changes in response to the B1 agonist des-arg9 bradykinin (DABK; 0.01-10µM) and B2 receptor agonist bradykinin (BK; 0.01-10µM) were quantified in all experiments. Leukocyte rolling was assessed as no. of cells passing a point each min. Following 4hr sepsis, there was a decrease in rolling in the WT: from 18 ± 4 (mean ± sem) to 2 ± 0.5 cells.min-1; and KO mice from 32 ± 8 to 1 ± 0.25 cells.min-1 (both p < 0.05). There was no difference in rolling in sepsis between WT and KO mice. Adhesion increased by 72% WT mice (from 3 ± 1 to 11 ± 1.4 cells/100µm segment; p < 0.05) and by 44% in KO mice (from 4.5 ± 1 to 8 ± 1.2 cells/100µm segment), but again there was no difference between WT and KO mice. Transmigration increased by 2-fold in WT mice (from 3 ± 0.25 to 6 ± 0.6 cells/100 µm2) and 1.2-fold in KO mice (from 3.5 ± 0.7 to 3 ± 0.5 cells.100µm-2). There was no permeability response to DABK in any mice. The permeability responses to 10µM BK was reduced by 51% in WT and by 62% in the KO mice at 4hr sepsis, but after 18hr sepsis permeability response increased by 57% in WT and 60% in KO mice. There was no difference between the 2 groups. At present, is not clear whether or not TRPV1 receptors play a protective role in sepsis in this vascular bed as TRPV1 deletion showed very similar inflammatory responses in both WT and KO mice.